validation: port some of the functionality to reana-commons

[audrium]

closes https://github.com/reanahub/reana-server/issues/442

This PR:

• Decoupled display_message() usage from the validation functionality
• Ported most of the validation logic to reana-commons. Except environment validation (which is optional and therefore can continue to be present in reana-client)
• Added reana-client validation wrappers (e.g. /validation/parameters.py) which calls the validation functionality from reana-commons and uses display_message() utility in the same way as it was done before
• Moved all validation functions to be present under /validation folder
• Separated load_reana_spec() validation and spec loading logic into separate functions. Renamed this function to load_validate_reana_spec() which now calls load_reana_spec() and validate_reana_spec().
• Ported load_reana_spec() to reana-commons

[codecov-commenter]

Codecov Report

Merging #594 (de892c7) into master (74ef7e6) will decrease coverage by 3.63%. The diff coverage is 83.19%.

@@            Coverage Diff             @@
##           master     #594      +/-   ##
==========================================
- Coverage   59.47%   55.84%   -3.64%     
==========================================
  Files          22       23       +1     
  Lines        2569     2258     -311     
==========================================
- Hits         1528     1261     -267     
+ Misses       1041      997      -44     

Impacted Files	Coverage Δ
reana_client/cli/cwl_runner.py	0.00% <0.00%> (ø)
reana_client/cli/utils.py	69.87% <ø> (-1.22%)	:arrow_down:
reana_client/config.py	100.00% <ø> (ø)
reana_client/errors.py	100.00% <ø> (ø)
reana_client/validation/environments.py	25.75% <40.00%> (ø)
reana_client/validation/compute_backends.py	78.57% <62.50%> (-18.73%)	:arrow_down:
reana_client/cli/workflow.py	62.12% <80.00%> (+0.06%)	:arrow_up:
reana_client/validation/utils.py	83.01% <83.01%> (ø)
reana_client/api/client.py	44.67% <100.00%> (ø)
reana_client/utils.py	70.96% <100.00%> (-2.27%)	:arrow_down:
... and 3 more